Arthropod-cell culture systems are developed from ticks and mosquitoes and applied to the study of vector-borne disease agents (arboviruses and rickettsias). These pathogens are tested for ability to propagate in the cultures and the susceptibilities of the cell systems are thus defined. After prolonged growth in vitro and at the relatively low temperatures required by insect cells, pathogens are tested for changes in strain, virulence, or antigenic characteristics. By contract with a collaborating laboratory overseas, arboviruses are studied from a standpoint of comparative dynamics of replication in vector and vertebrate cells. BIBLIOGRAPHIC REFERENCES: Bhat, U. K. M. and Yunker, C. E.: Susceptibility of a tick cell line (Dermacentor parumapertus Neumann) to infection with arboviruses. Proc. 2nd International Symposium on Arctic Arboviruses, Mont Gabriel, Que., Canada, May 26-28, 1977. In press.